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SubjectRe: [PATCH] WARN_ONCE(): use bool for boolean flag
Daniel Walker escreveu:
> On Sun, 2009-09-27 at 12:56 -0300, Cesar Eduardo Barros wrote:
>> Daniel Walker escreveu:
>>> On Sun, 2009-09-27 at 10:53 -0300, Cesar Eduardo Barros wrote:
>>>> #define
>>>> WARN_ON_ONCE(condition) ({ \
>>>> - static int __warned; \
>>>> + static bool __warned; \
>>>> int __ret_warn_once = !!(condition); \
>>> Could __ret_warn_once be bool also ? It looks like just another
>>> conditional variable..
>> Yes, it could (as long as either it is converted back to int in the
>> return of the macro, or all users do not care about the macro's return
>> type). However, the justification used for the printk_once patch (and
>> this WARN_ONCE patch) does not apply directly anymore, since the code is
>> different (to start with, it is not a static variable).
>
> I did a couple kernel builds to test this on a small normal config,
>
> vmlinux.base-line
> text data bss dec hex filename
> 6718958 497200 1082460 8298618 7ea07a vmlinux.base-line
>
> vmlinux.one-bool <-- Your patch
> text data bss dec hex filename
> 6718590 497232 1082292 8298114 7e9e82 vmlinux.one-bool

I am still trying to understand why data increases (but not enough to
offset the gains on text and bss). My own testing had the same
qualitative result (x86-64 defconfig):

text data bss dec hex filename
8101271 1207116 992764 10301151 9d2edf vmlinux.warn.before
8100553 1207148 991988 10299689 9d2929 vmlinux.warn.after

> vmlinux.all-bool-converted
> text data bss dec hex filename
> 6718506 497232 1082292 8298030 7e9e2e vmlinux.all-converted
>
> your changes drops the size 368 bytes, and if you convert the other
> conditionals it drops it by another 84 bytes. Not much more, but it's
> something.
>
> So I think Rolands original reasoning still holds.. As far as people
> needing an int output from WARN_ON() , I'm not sure that's happening
> anyplace .. I can't imagine a sane usage for that..

I took a quick look, and all uses seem to be directly in a boolean
context (within an if()), so there would be no problem. Besides, the
unlikely() all these macros end with does a double negation, meaning
even if it is an int, it will be either 0 or 1 (but I am not sure I am
reading these macros right - it seems CONFIG_TRACE_BRANCH_PROFILING
turns all unlikely() into likely()).
In fact, I was expecting no change at all, since gcc should be able to
see it is being treated as a boolean (perhaps I am trusting gcc too
much). And to make matters even more confusing, my own test changing all
__ret_warn_once to bool and dropping the !! caused an _increase_ of 598
bytes (x86-64 defconfig).

text data bss dec hex filename
8100553 1207148 991988 10299689 9d2929 vmlinux.warnret.before
8101119 1207180 991988 10300287 9d2b7f vmlinux.warnret.after

(And yes, data increased again.)

--
Cesar Eduardo Barros
cesarb@cesarb.net
cesar.barros@gmail.com


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